Recent electrophysiological (Hubel and Wiesel, 1974) and psychophysical (Virsu, et al., 1979) investigations suggest an important unifying principle of anatomical homogeneity, expecially with regard to photopic vision: The spatial resolution of any visual function is predicted by its cortical and not its retinal subtense. Therefore, it is dictated by the reciprocal of the cortical magnification factor, a term which appears to grow linearly with retinal eccentricity. The aim of this proposal is to examine this concept and to generalize it as widely as possible. To accomplish this goal we will measure the upper acuity limit for sinusoidal gratings at various eccentricities, scaling the area of the stimulus to cover an equivalent cortical surface area. This will establish the minimum angle of resolution for each retinal area and is presumed to be the best estimate of cortical magnification. Then we will determine whether these estimates can be used to predict the spatial grain of other tasks with retinal eccentricity including vernier acuity, movement acuity, stereoscopic acuity, and binocular fusional limits. To the extent that these differing psychopysical functions can be predicted from the grating acuity limit, they will support the concept of functional cortical homogeneity. This will subsume a large class of psychophysical and anatomical results into a common metric. If some visual tasks show a different magnification function, it would indicate that they are subserved by secondary projection areas. Such a classification will aid in the functional dissection of the hierarchy of mechanisms mediating higher visual processes.